Process for Removing Nitrogen Compounds from a Hydrocarbon Stream

ABSTRACT

Disclosed is a process for removing nitrogen from a hydrocarbon feed stream by contacting the hydrocarbon feed stream with an adsorbent at nitrogen removal conditions to produce a hydrocarbon effluent stream having a lower nitrogen content relative to the hydrocarbon feed stream. The hydrocarbon feed stream comprises an aromatic compound, an organic nitrogen compound, and a diolefin compound.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of U.S. Provisional Application No. 61/247,261 filed Sep. 30, 2009.

FIELD OF THE INVENTION

This invention relates to a process for removing nitrogen compounds from a hydrocarbon stream. More particularly, this invention relates to the use of a selective adsorption process for removing nitrogen compounds from a hydrocarbon stream.

BACKGROUND OF THE INVENTION

The use of molecular sieves as catalysts in aromatic conversion processes are well known in the chemical processing and refining industry. Aromatic conversion reactions of considerable commercial importance include the alkylation of aromatic compounds such as in the production of ethyltoluene, xylene, ethylbenzene, cumene, or higher alkyl aromatics and in disproportionation reactions such as toluene disproportionation, xylene isomerization, or the transalkylation of polyalkylbenzenes to monoalkylbenzenes. Often the feedstock to such an aromatic conversion process will include an aromatic component or alkylation substrate, such as benzene, and a C₂ to C₂₀ olefin alkylating agent or a polyalkyl aromatic hydrocarbon transalkylating agent. In the alkylation zone, the aromatic feed stream and the olefinic feed stream may be reacted over an alkylation catalyst to produce alkylated aromatics, e.g. cumene or ethylbenzene. A portion or all of the alkylation substrate may be provided by other process units including the separation section of a styrene process unit. Polyalkylated benzenes are separated from monoalkylated benzene product and recycled to a transalkylation zone and contacted with benzene over a transalkylation catalyst to yield monoalkylated benzenes and benzene.

Catalysts for aromatic conversion processes generally comprise zeolitic molecular sieves. Examples include, zeolite beta (U.S. Pat. No. 4,891,458); zeolite Y, zeolite omega and zeolite beta (U.S. Pat. No. 5,030,786); X, Y, L, B, ZSM-5 and Omega crystal types (U.S. Pat. No. 4,185,040); X, Y, ultrastable Y, L, Omega, and mordenite zeolites (U.S. Pat. No. 4,774,377); and UZM-8 zeolites (U.S. Pat. No. 6,756,030 and U.S. Pat. No. 7,091,390). It is known in the art that the aromatic feed stream to aromatic conversion processes often contains nitrogen compounds, including weakly basic organic nitrogen compounds such as nitriles, that can, even at ppm and ppb levels, cumulatively act to poison the downstream aromatic conversion catalysts such as aromatic alkylation catalysts and significantly shorten their useful life. Use of a variety of zeolitic or molecular sieve guard beds to remove one or more types of nitrogen compounds from an aromatic hydrocarbon stream upstream of an aromatic conversion process are known in the art. Examples include: U.S. Pat. No. 7,205,448; U.S. Pat. No. 5,220,099; WO 00/35836; WO 01/07383; U.S. Pat. No. 4,846,962; U.S. Pat. No. 6,019,887; and U.S. Pat. No. 6,107,535. U.S. Pat. No. 7,205,448 discloses an acidic molecular sieve adsorbent preferentially adsorbs water and basic organic nitrogen compounds over weakly basic organic nitrogen compounds such as nitrites at lower temperatures and elevated temperatures improve the capacity of acidic molecular sieve adsorbents to adsorb nitrites in the presence of water.

It has recently been discovered that unsaturated aliphatic hydrocarbons such as olefinic compounds, and particularly diolefins, can shorten the effective life of adsorbents, e.g. nitrogen adsorptive zeolites or molecular sieves, used in nitrogen guard beds that are applied to various process streams, including aromatic hydrocarbon feeds upstream of an aromatic conversion process such as alkylation. These unsaturated aliphatic, e.g. olefinic, compounds are present in aromatic process streams contaminated with nitrogen compounds, including benzene streams generated in styrene process separation sections and other streams requiring removal of the nitrogen compounds prior to being contacted with a catalyst or other material susceptible to nitrogen poisoning. The presence, in particular, of highly unsaturated olefinic compounds, e.g. C₄-C₆ diolefins, in aromatic streams having nitrogen compound contaminants, adversely impacts the performance of nitrogen adsorptive materials. Without being bound by theory, it is believed that the olefinic compounds and/or other unsaturated aliphatic compounds may shorten the life of the nitrogen adsorbent by competing with the nitrogen compounds for the adsorption sites and/or reacting, e.g. with aromatics such as benzene, to form heavy reaction products that deposit on the nitrogen guard bed adsorbent.

SUMMARY OF THE INVENTION

The invention relates to methods for removing nitrogen compounds from a hydrocarbon stream while minimizing the adsorption and/or reaction of unsaturated aliphatic compounds, e.g. olefins and diolefins that are present in the hydrocarbon stream. The invention enables longer adsorbent life which minimizes the need to regenerate or replace the adsorbent. The invention may also be used in existing guard bed systems without the need for additional equipment.

In an embodiment, the invention is a process for removing nitrogen from a hydrocarbon feed stream comprising an aromatic compound, an organic nitrogen compound, and a diolefin compound, the process comprising: contacting the hydrocarbon feed stream with an adsorbent at nitrogen removal conditions to produce a hydrocarbon effluent stream having a lower nitrogen content relative to the hydrocarbon feed stream.

In an embodiment, the adsorbent comprises a zeolite component, an alumina component and a metal component (Madd); the alumina component ranging an amount from about 40 wt % to about 90 wt % of the adsorbent, and the metal component ranging in an amount from about 0.015 moles to 0.08 moles of the metal as the oxide per 100 g of the adsorbent.

In an embodiment, the process has a nitrogen to diolefin removal greater than 1 on a relative mass percent basis. In another embodiment, a diolefin content of the hydrocarbon effluent stream is at least 30% of the diolefin content of the hydrocarbon feed stream. In a further embodiment, a nitrogen content of the hydrocarbon effluent stream is no more than about 50% of the nitrogen content of the hydrocarbon feed stream and a diolefin content of the hydrocarbon effluent stream is at least 30% of the diolefin content of the hydrocarbon feed stream.

DETAILED DESCRIPTION OF THE INVENTION

The invention relates to methods for removing nitrogen from a hydrocarbon feed stream comprising contacting the hydrocarbon feed stream with an adsorbent at nitrogen removal conditions to produce a hydrocarbon effluent stream having a lower nitrogen content relative to the hydrocarbon feed stream. The hydrocarbon feed stream of the invention comprises an aromatic compound, an organic nitrogen compound and a diolefin compound. In an embodiment, the aromatic hydrocarbon may be selected from the group consisting of benzene, naphthalene, anthracene, phenanthrene, and substituted derivatives thereof, with benzene and its derivatives being preferred aromatic compounds. The aromatic compound may have one or more of the substituents selected from the group consisting of alkyl groups having from 1 to about 20 carbon atoms, hydroxyl groups, and alkoxy groups whose alkyl group also contains from 1 up to 20 carbon atoms. Where the substituent is an alkyl or alkoxy group, a phenyl group can also be substituted on the alkyl chain.

Although unsubstituted and monosubstituted benzenes, naphthalenes, anthracenes, and phenanthrenes are most often used in the practice of this invention, polysubstituted aromatics also may be employed. Examples of suitable alkylatable aromatic compounds in addition to those cited above include biphenyl, toluene, xylene, ethylbenzene, propylbenzene, butylbenzene, pentylbenzene, hexylbenzene, heptylbenzene, octylbenzene, etc.; phenol, cresol, anisole, ethoxy-, propoxy-, butoxy-, pentoxy-, hexoxybenzene, and so forth. Sources of benzene, toluene, xylene, and or other feed aromatics include product streams from naphtha reforming units, aromatic extraction units, recycle streams from styrene monomer production units, and petrochemical complexes for the producing para-xylene and other aromatics. The hydrocarbon feed stream may comprise more one or more aromatic hydrocarbon compounds. In an embodiment, the concentration of aromatic hydrocarbons in the hydrocarbon feed stream ranges from about 5 mass % to about 99.9 mass % of the hydrocarbon feed. The hydrocarbon feed stream may comprise between about 50 mass % and about 99.9 mass % benzene.

The hydrocarbon feed stream comprises one or more organic nitrogen compounds. Organic nitrogen compounds typically include a larger proportion of basic nitrogen compounds such as indoles, pyridines, quinolines, diethanol amine (DEA), morpholines including N-formyl-morpholine (NFM) and N-methyl-pyrrolidone (NMP). Organic nitrogen compounds may also include weakly basic nitriles, such as acetonitrile, propionitrile, acrylonitrile, and mixtures thereof. The basic organic nitrogen compounds are adsorbed well on conventional clay or resin adsorbent guard beds. Thus, the invention does not require but encompasses use of an optional basic nitrogen adsorption zone containing an adsorbent to remove basic organic nitrogen compounds from the hydrocarbon stream as is known in the art.

In an embodiment, the concentration of organic nitrogen compounds in the hydrocarbon feed ranges from about 30 ppb-wt (parts per billion by weight) to about 1 mole % of the hydrocarbon feed; the concentration of organic nitrogen compounds may range from about 100 ppb-wt to about 100 ppm-wt (parts per million by weight) of the hydrocarbon feed. In an embodiment, the concentration of weakly basic organic nitrogen compounds such as nitriles in the hydrocarbon feed ranges from about 30 ppb-wt to about 100 ppm-wt of the hydrocarbon feed;

The hydrocarbon feed stream comprises one or more diolefin compounds, including for example diolefins having 4 to 6 carbon atoms per molecule, i.e. C₄ to C₆ diolefins. In an embodiment, the concentration of diolefin compounds in the hydrocarbon feed ranges from about 30 ppb-wt to about 3000 ppm-wt of the hydrocarbon feed; and the concentration of diolefin compounds may range from about 50 ppb-wt to about 2000 ppm-wt of the hydrocarbon feed. The hydrocarbon feed stream may comprise other olefins such as mono-olefins. Typically, the overall concentration of all olefins in the hydrocarbon feed stream will be no more than 1.0 wt-% olefins. The hydrocarbon stream may contain water up to and beyond saturation conditions.

Adsorbents used in the instant invention and methods of making the adsorbents are disclosed in U.S. Pat. No. 6,632,766, which is herein incorporated by reference in its entirety. In brief, the adsorbent comprises a zeolite component, an alumina component and a metal component wherein the alumina component is present in an amount from about 40 to about 90 wt % of the adsorbent and the metal component is present in an amount from about 0.015 to 0.08 moles of the metal as the oxide per 100 g of the adsorbent and may be referred to as a nitrogen selective adsorbent.

Zeolites which can be used in the adsorbent have a pore opening of about 5 to about 10 Å and in general have a composition represented by the empirical formula:

M_(2/n)O:Al₂O₃ :bSiO₂

Where M is a cation having a valence of “n” and “b” has a value of about 2 to about 500. In an embodiment, zeolites are those that have a SiO₂/Al₂O₃ molar ratio of about 2:1 to about 6:1 and/or those having the crystal structure of zeolite X, faujasite, zeolite Y, zeolite A, mordenite, beta and ferrierite. Preferred zeolites are zeolites X, Y and A. In an embodiment, the zeolite is 13× zeolite.

The alumina component is an activated alumina that may be obtained by rapid dehydration of aluminum hydroxides, e.g., alumina trihydrate, gibbsite, or hydrargillite in a stream of hot gasses or solid heat carrier. Dehydration may be accomplished in any suitable apparatus using the stream of hot gases or solid heat carrier. Generally, the time for heating or contacting with the hot gases is typically from a fraction of a second to 4 or 5 seconds. The temperature of the gases normally varies between 400° C. and 1000° C. The process is commonly referred to as flash calcination and is disclosed, for example in U.S. Pat. No. 2,915,365. However, other methods of calcination may be employed. One source of activated alumina is gibbsite which is one form of alumina hydrate derived from bauxite using the Bayer process. However, alpha alumina monohydrate, pseudoboehmite or the alumina trihydrate may be used if sufficiently calcined. Other sources of alumina may also be utilized including clays and alumina alkoxides. Activated aluminas include aluminas having a surface area usually greater than 100 m²/g and typically in the range of 100 to 400 m²/g.

The metal component (Madd) is selected from the group consisting of alkali, alkaline earth metals, and mixtures thereof. The metal component (Madd) is in addition to the metal cation (M) present in the exchange sites of the zeolite. Additionally, the metal component can be the same or different than the M metal. For example, the M metal in a zeolite can be potassium whereas the metal component (Madd) can be sodium. Examples of the metal component (Madd) include but are not limited to sodium, potassium, lithium, rubidium, cesium, calcium, strontium, magnesium, barium, zinc and copper. In an embodiment, the metal component (Madd) is selected from the group consisting of sodium, potassium, lithium, rubidium, cesium and mixtures thereof. The source of the metal component can be any compound which decomposes to the metal oxide at activation conditions. Examples of metal component sources are the nitrates, hydroxides, carboxylates, carbonates and oxides of the metals. The shaped adsorbent can be prepared by combining the three components in any order and forming into a shaped article. Without wishing to be bound by any particular theory, it is believed that the metal component (Madd) decreases the acidity of zeolite and/or alumina components. Thus, the acidity/basicity of the adsorbent may be varied by the amount and type of metal component (Madd). For example having more metal component (Madd) and/or using metals that provide more basic metal oxides such as potassium and cesium will increase the basicity, i.e. reduce the acidity, of the adsorbent. Excessive amounts of the metal component (Madd) may be detrimental if sufficient to accelerate the double bond shift reaction of the olefins.

In one method, the alumina, zeolite and an aqueous solution of the desired metal compound are mixed and formed into a shaped article. For example, gamma alumina, zeolite X and a solution of sodium acetate can be combined into a dough and then extruded or formed into shapes such as pellets, pills, tablets or spheres (e.g. by the oil drop method) by means well known in the art. A preferred method of forming substantially rounded shapes or bodies involves the use of a pan nodulizer. This technique uses a rotating pan or pan nodulizer onto which is fed the alumina component, zeolite component and a solution of the metal component thereby forming substantially rounded particles.

Another method of forming the shaped article is to mix powders of the alumina, zeolite and metal compound followed by formation of pellets, pills, etc. A third method is to combine the alumina and zeolite components (powders), form them into a shaped article and then impregnate the shaped article with an aqueous solution of the metal compound. The forming step is carried out by any of the means enumerated above.

In preparing a solution of the desired metal compound, pH may be adjusted to a value from about 7 to about 14. In an embodiment, the pH ranges from about 9 to about 13.5. The pH of the solution may be controlled by adding the appropriate amount of the desired metal hydroxide. For example, if sodium is the desired metal, sodium acetate can be used to form the aqueous solution and the pH may be adjusted using sodium hydroxide.

Having obtained the shaped articles, they are cured or dried at ambient temperature up to about 200° C. for a time of about 5 minutes to about 25 hours. The shaped articles can be cured in batches e.g. bins or trays or in a continuous process using conventional equipment such as a moving belt oven, or rotating kiln. Once the shaped articles are cured, they are activated by heating the cured articles at a temperature of about 275° C. to about 600° C. for a time of about 5 to about 70 minutes. The heating can be done with the articles in a moving pan or in a moving belt oven or a rotating kiln where the articles may be direct fired or indirect fired to provide the finished solid adsorbent.

The relative amount of the three components can vary considerably over a wide range. Usually the amount of alumina varies from about 40 to about 90 wt % of the adsorbent. In an embodiment, the mass ratio of the alumina component to the zeolite component in the adsorbent ranges from about 18:1 to about 2:3; and may range from about 9:1 to about 2:3. The amount of zeolite may vary from about 5 to about 60 wt % of the adsorbent. The amount of metal component, Madd, can also vary considerably, but must be present in an amount equal to at least 10% of the stoichiometric amount of the metal cation, M, present in the exchange sites of the zeolite. For practical reasons, the maximum amount of Madd should be no more than 50% of the stoichiometric amount of M. In absolute terms, it is preferred that the amount of Madd be present from about 0.015 to about 0.08 moles of Madd per 100 grams of adsorbent. The amounts of M and Madd are reported or expressed as the oxide of the metal, e.g. Na₂O.

The hydrocarbon feed stream to be purified is contacted with the above described adsorbent at nitrogen removal conditions to reduce the nitrogen content of the hydrocarbon stream. The process produces an effluent hydrocarbon stream having a lower nitrogen content relative to the nitrogen content of the hydrocarbon feed stream. In general, nitrogen removal conditions include a temperature from about 25° C. to about 300° C. and a pressure from about 34.5 kPa(g) to about 4136.9 kPa(g). In an embodiment, the temperature ranges from about 50° C. to about 200° C.; and the temperature may range from about 75° C. to about 175° C. The effluent hydrocarbon stream from the adsorption zone, may then be introduced into a downstream processing unit such as an alkylation zone or transalkylation zone.

It may be desirable to use a first bed of an alkylation zone or transalkylation zone as an adsorbent zone for the removal of nitrogen. In such an event, the adsorbent and the alkylation or transalkylation catalyst should be spaced apart. The alkylation agent, e.g. olefin, should bypass the adsorption zone and be delivered to an interbed space to mix with the denitrogenated hydrocarbon stream exiting the adsorption zone. However, it may be preferable to contain the nitrogen adsorption zone and the alkylation zone in separate vessels.

In an embodiment, the invention removes a greater amount of nitrogen from the hydrocarbon feed stream than the amount of unsaturated aliphatic compounds removed on a relative percent basis. The relative percent basis is determined by the nitrogen content and Bromine Index of the hydrocarbon feed and effluent streams. Bromine Index is commonly used to assess the olefin content, including diolefins, of hydrocarbon mixtures. That is, in this embodiment, the percent decrease in nitrogen content on a mass percent basis is greater than the percent decrease of the Bromine Index between the hydrocarbon feed and effluent streams. For example, if the hydrocarbon feed stream contains 4 ppm-wt nitrogen and has a Bromine Index of 300 and the hydrocarbon effluent stream contains 1 ppm-wt nitrogen and has a Bromine Index of 150, the nitrogen content is decreased by 75% ((4-1)/4) and the Bromine Index is decreased by 50% ((300-150)/300). Therefore, in this example, the process has a nitrogen to unsaturated aliphatic compound removal of 1.5 (75%/50%) on a relative percent basis. Since the nitrogen to unsaturated aliphatic compound removal is greater than 1, the amount of nitrogen removed from the hydrocarbon feed stream is greater than the amount of unsaturated aliphatic compounds removed from the hydrocarbon feed stream on a relative percent basis. In another embodiment, the nitrogen to unsaturated aliphatic compound removal is at least 1.5 on a relative percent basis, and the nitrogen to unsaturated aliphatic compound removal may be at least 2 on a relative percent basis. In a further embodiment, the nitrogen to unsaturated aliphatic compound removal is at least 2.5 on a relative percent basis, and the nitrogen to unsaturated aliphatic compound removal may be at least 3 on a relative percent basis.

In an embodiment, the invention removes a greater amount of nitrogen from the hydrocarbon feed stream than the amount of diolefin compounds removed from the hydrocarbon feed stream on a relative mass percent basis. That is, in this embodiment, the percent decrease in nitrogen content on a mass percent basis is greater than the percent decrease of the diolefin content on a mass percent basis between the hydrocarbon feed and effluent streams, i.e. the nitrogen to diolefin removal is greater than 1 on a relative mass percent basis. In another embodiment, the nitrogen to diolefin removal is at least 1.5 on a relative mass percent basis; and the nitrogen to diolefin removal may be at least 2 on a relative mass percent basis. In a further embodiment, the nitrogen to diolefin removal is at least 2.5 on a relative mass percent basis; and the nitrogen to diolefin removal may be at least 3 on a relative mass percent basis.

Removal of the unsaturated aliphatic compounds such as olefin and/or diolefin compounds may result from various mechanism including adsorption and reaction. The nitrogen content of the hydrocarbon feed stream to and effluent stream from the adsorption zone may be determined by standard lab methods such as UOP269 or ASTM D5762 or ASTM D4629 depending on the nitrogen concentration. Likewise, the diolefin content of the streams may be determined by method UOP980, and the Bromine Index of the streams may be determined using method UOP304. Unless otherwise noted, the analytical methods used herein such as ASTM D5762 and UOP980 are available from ASTM International, 100 Barr Harbor Drive, West Conshohocken, Pa., USA.

In another embodiment, at least 50 wt % of the nitrogen is removed from the hydrocarbon feed stream on an elemental basis; and the invention may remove at least about 70 wt % of the nitrogen in the hydrocarbon feed stream on an elemental basis. In another embodiment, at least about 80 wt % of the nitrogen is removed from the hydrocarbon feed stream on an elemental basis, that is, the hydrocarbon effluent stream from the contacting step has a nitrogen content that is no more than about 20% of the nitrogen content of the hydrocarbon feed stream.

In a further embodiment, the hydrocarbon effluent stream from the contacting step has a diolefin content of at least 30% of the diolefin content of the hydrocarbon feed stream; and the hydrocarbon effluent stream may have a diolefin content of at least 50% of the diolefin content of the hydrocarbon feed stream. In another embodiment, the hydrocarbon effluent stream has a diolefin content of at least 70% of the diolefin content of the hydrocarbon feed stream.

In another embodiment, the hydrocarbon effluent stream from the contacting step has a nitrogen content no more than about 50% of the nitrogen content of the hydrocarbon feed stream, and hydrocarbon effluent stream has a diolefin content of at least 30% of the diolefin content of the hydrocarbon feed stream. In a further embodiment, the hydrocarbon effluent stream from the contacting step has a nitrogen content no more than about 50% of the nitrogen content of the hydrocarbon feed stream, and hydrocarbon effluent stream has a diolefin content of at least 50% of the diolefin content of the hydrocarbon feed stream. The hydrocarbon effluent stream from the contacting step may have a nitrogen content no more than about 30% of the nitrogen content of the hydrocarbon feed stream, and hydrocarbon effluent stream may have a diolefin content of at least 30% of the diolefin content of the hydrocarbon feed stream. The hydrocarbon effluent stream from the contacting step may have a nitrogen content no more than about 30% of the nitrogen content of the hydrocarbon feed stream, and hydrocarbon effluent stream may have a diolefin content of at least 50% of the diolefin content of the hydrocarbon feed stream.

Example 1

An adsorbent according to the invention was prepared following Example 2 of U.S. Pat. No. 7,115,154. The resulting adsorbent was found to have 0.142 total moles of Na₂O per 100 g of adsorbent. The total moles includes the metal component (Madd) added of 0.036 moles of Na₂O per 100 g of adsorbent.

Example 2

A commercially available acid treated clay was obtained from Sud-Chemie under the product name TONSIL CO 630 G for use as a comparative adsorbent.

Example 3

A sample of Y-74 zeolite was slurried in a 15 wt % NH₄NO₃ aqueous solution and the solution temperature was brought up to 75° C. (167° F.). Y-74 zeolite is a stabilized sodium Y zeolite with a bulk Si/Al₂ ratio of approximately 5.2, a unit cell size of approximately 24.53, and a sodium content of approximately 2.7 wt % calculated as Na₂O on a dry basis. Y-74 zeolite is prepared from a sodium Y zeolite with a bulk Si/Al₂ ratio of approximately 4.9, a unit cell size of approximately 24.67, and a sodium content of approximately 9.4 wt % calculated as Na₂O on a dry basis that is ammonium exchanged to remove approximately 75% of the Na and then steam de-aluminated at approximately 600° C. (1112° F.) by generally following steps (1) and (2) of the procedure described in col. 4, line 47 to col. 5, line 2 of U.S. Pat. No. 5,324,877. After 1 hour of contact at 75° C. (167° F.), the slurry was filtered and the filter cake was washed with an excessive amount of warm de-ionized water. These NH₄ ⁺ ion exchange, filtering, and water wash steps were repeated two more times, and the resulting filter cake had a bulk Si/Al₂ ratio of 5.2, a sodium content of 0.13 wt % calculated as Na₂O on a dry basis, a unit cell size of the 24.572 Å and an absolute intensity of 96 as determined X-ray diffraction. The resulting filter cake was dried to an appropriate moisture level, mixed with HNO₃-peptized Pural SB alumina to give a mixture of 80 parts by weight of zeolite and 20 parts by weight Al₂O₃ binder on a dry basis, and then extruded into 1.6 mm diameter cylindrical extrudate. The extrudate was dried and calcined at approximately 600° C. for one hour in flowing air. This catalyst was representative of the existing art. This catalyst had a unit cell size of 24.494 Å, an XRD absolute intensity of 61.1, and 57.2% framework aluminum as a percentage of the aluminum in the modified Y zeolite.

Example 4

A sample of a commercial benzene recycle stream (>99 wt % benzene) containing olefin, diolefin and nitrogen compounds was used as the hydrocarbon feed to evaluate the effectiveness of the adsorbents of Examples 1-3 to remove nitrogen and the unsaturates. The analysis of the feed is reported in Table 1 with the analysis of the effluent or product from each test. The unsaturated aliphatic, i.e., total olefin content was determined by UOP304. The nitrogen content was determined by D4629, and the diolefin content was determined by UOP980 as modified to improve the sensitivity of the method to detect lower levels of diolefins. UOP980 was followed except that sample size was altered and standard solutions of lower concentrations were used during calibration of the instrument as known by those skilled in the art to improve detection of lower concentrations of the diolefins in the samples. The modification of UOP980 does not alter the relative measurements between different samples, but improves and/or enables quantification of concentrations of less than 500 ppm-wt and especially less than 100 ppm-wt of diolefins.

Prior to the test, the adsorbent was pre-dried at 250° C. for 4 hours in flowing nitrogen. The adsorption experiment was done in an autoclave, which was first purged with nitrogen followed by charging 0.6 g of adsorbent and 30 g of the hydrocarbon feed. The autoclave was then pressurized to about 400 psig and ramped to the temperature listed in Table 1 for each test. The autoclave includes a mixer which was set at 100 rpm. When the specified temperature was reached, the autoclave was held at temperature for one hour with mixing. Thereafter, the heat was cut to allow the autoclave to cool to room temperature and mixing stopped. The spent adsorbent was separated from the liquid product or effluent, which was sampled and analyzed.

TABLE 1 Feed Example 1 Example 2 Example 3 Temperature, ° C. 100 125 150 100 125 150 25 75 125 Nitrogen, ppm-wt 3.1 0.7 0.7 0.6 1.32 1.06 0.7 0.9 1.41 0.6 Bromine Index, 292 225 209 258 138 91 47 114 91 23 mg Br per 100 g Diolefins, ppm-wt 825 614 621 613 25 3 1 NA 247 5

Example 1 according to the invention exhibited unexpected effectiveness in removing nitrogen while leaving the olefin and diolefin compounds relatively intact. The ability to selectively adsorb nitrogen components over olefin components makes the adsorbent particularly useful in commercial services, where both types of contaminants are present in aromatic streams. By minimizing adsorption and/or reaction of the olefins a higher nitrogen capacity and longer adsorbent life are expected. 

1. A process for removing nitrogen from a hydrocarbon feed stream comprising an aromatic compound, an organic nitrogen compound, and a diolefin compound, the process comprising: contacting the hydrocarbon feed stream with an adsorbent at nitrogen removal conditions to produce a hydrocarbon effluent stream having a lower nitrogen content relative to the hydrocarbon feed stream; wherein the adsorbent comprises a zeolite component, an alumina component and a metal component (Madd); the alumina component ranging an amount from about 40 wt % to about 90 wt % of the adsorbent, and the metal component ranging in an amount from about 0.015 moles to 0.08 moles of the metal as the oxide per 100 g of the adsorbent.
 2. The process of claim 1 wherein the zeolite component comprises an X zeolite.
 3. The process of claim 1 wherein a mass ratio of the alumina component to the zeolite component in the adsorbent ranges from about 18:1 to about 2:3.
 4. The process of claim 1 wherein the metal component (Madd) is an alkali metal selected from the group consisting of sodium, potassium, lithium, rubidium, cesium and mixtures thereof.
 5. The process of claim 1 wherein the aromatic compound is benzene and is present in an amount ranging from about 5 mass % to about 99.9 mass % of the hydrocarbon feed stream.
 6. The process of claim 1 wherein the organic nitrogen compound is selected from the group consisting of basic nitrogen compounds, weakly basic nitriles, and combinations thereof.
 7. The process of claim 6 wherein the organic nitrogen compound is present in an amount ranging from about 30 ppb-wt to about 1 mole % of the hydrocarbon feed stream.
 8. The process of claim 6 wherein the organic nitrogen compound is weakly basic nitriles and is present in an amount ranging from about 30 ppb-wt to about 100 ppm-wt of the hydrocarbon feed stream.
 9. The process of claim 1 wherein the diolefin compound comprises at least one of a C₄ diolefin, a C₅ diolefin, and a C₆ diolefin; and the diolefin compound is present in an amount ranging from about 30 ppb-wt to about 3000 ppm-wt of the hydrocarbon feed stream.
 10. The process of claim 1 wherein the nitrogen removal conditions include a temperature from about 25° C. to about 300° C. and a pressure from about 34.5 kPa(g) to about 4136.9 kPa(g).
 11. The process of claim 1 wherein a nitrogen to unsaturated aliphatic compound removal is greater than 1 on a relative percent basis.
 12. The process of claim 1 wherein a nitrogen to diolefin removal is greater than 1 on a relative mass percent basis.
 13. The process of claim 1 wherein a nitrogen to diolefin removal is at least 1.5 on a relative mass percent basis.
 14. The process of claim 1 wherein a nitrogen to diolefin removal is at least 2 on a relative mass percent basis.
 15. The process of claim 1 wherein at least about 50 wt % of the nitrogen is removed from the hydrocarbon feed stream on an elemental basis.
 16. The process of claim 1 wherein at least about 70 wt % of the nitrogen is removed from the hydrocarbon feed stream on an elemental basis.
 17. The process of claim 1 wherein a diolefin content of the hydrocarbon effluent stream is at least 30% of the diolefin content of the hydrocarbon feed stream.
 18. The process of claim 1 wherein a diolefin content of the hydrocarbon effluent stream is at least 50% of the diolefin content of the hydrocarbon feed stream.
 19. The process of claim 1 wherein a nitrogen content of the hydrocarbon effluent stream is no more than about 50% of the nitrogen content of the hydrocarbon feed stream and a diolefin content of the hydrocarbon effluent stream is at least 30% of the diolefin content of the hydrocarbon feed stream.
 20. The process of claim 1 wherein a nitrogen content of the hydrocarbon effluent stream is no more than about 50% of the nitrogen content of the hydrocarbon feed stream and a diolefin content of the hydrocarbon effluent stream is at least 50% of the diolefin content of the hydrocarbon feed stream. 